No. You can not use HTML tags in any field except body of the message.
The maintainer of the script has the option of allowing or
disallowing any HTML in the Message part of your posting. If
they disallow it, the script will just throw out everything in
<>'s. If they allow it, your html markup will appear in
the posting. It can't hurt to try.

Colons appear in the message dialog box when you try to followup up on a
message to indicate that those lines are quoting the previous document.
The owner of the WWWBoard can decide whether they wish to enable or
disable the quoting of previous messages.